Adding Electrical Accessories to your Motorcycle

If you’re reading this it’s a good bet your favorite form of transportation is a motorcycle, not a car. Even diehard motorcyclists, however, admit there are situations in which some of the comforts of a four-wheeler—heat, music and driving lights—come in handy.

But while adding one or two accessories to your motorcycle is fairly simple, the more circuits you add the greater the potential not only for creating an unsightly maze of wiring sprouting from under your bike’s seat, but draining the battery and overloading the electrical system, as well.

Before you do anything, you need to determine just how much of a drain you can put on your bike’s electrical system without overloading it. If your bike has ever been tested in Rider, look in the spec chart to find the alternator output in watts. You can sometimes also find this information in the shop manual. Let’s say your bike puts out 400 watts maximum. Bear in mind that’s 400 watts at a given rpm, often corresponding to highway speeds in top gear. At lower rpm, such as trolling through town in traffic, the output will be lower.

More light is good, especially at night in deer country. Too much electrical draw, however, will leave you in the dark.

Next, determine how many watts are consumed running things like lights. Does your bike have one headlight (55 watts) or two (110 watts)? Subtract that from 400, since both headlights are always on. Do the same with the taillight, instrument lights and running lights. These small bulbs don’t use a lot of power, but they add up. Check your shop manual for each bulb’s specifications. Some things, like fuel injection and fuel pumps, will be harder to pin down, and might not be in the manual. But odds are the draw is pretty small.

Now that you know roughly how much of your alternator’s output is used just running the bike, you can tell how much you have left to run accessories. Let’s say you determine that 150 of the 400 watts is accounted for, leaving you 250 watts. An electric vest consumes about 45 watts at full power. A pair of 35-watt driving lights uses another 70. That leaves you a 135-watt surplus, which is a safe margin. Add another vest for your passenger, though, and heated gloves for yourself (about 20 watts per pair) and you’re pushing your luck. Around town or at low rpm you should turn down or switch off some or all of the add-ons to avoid draining your bike’s battery. Even at high rpm and maximum output, you’ll be operating close enough to the edge to put a strain on the electrical system.

Writing each socket’s function on a label helps make troubleshooting easier.

Once you’ve done the necessary math, hooking everything up comes next. In theory, the easiest way to power an electrical accessory is to connect it to the battery, negative to negative and positive to positive. But there are two drawbacks to this meth­od. First, the power is always on, even when the ignition’s not, so if you walk away without turning the accessory off, you could come back to a dead battery. Second, you can only attach so many terminals to the battery before you wind up with a confusing tangle of wires that makes it difficult to troubleshoot shorts and blown fuses.

The solution is a power distribution block. Electrical Connection (www.electricalconnection.com) makes three models, one each for GL1500 and GL1800 Gold Wings, and a universal one you can use on just about any bike. They’re hooked up to the battery terminals, but are also connected to the ignition circuit through a relay so the accessories are only powered when the ignition’s on. The universal model has terminals for six accessories, uses common blade-type fuses, and is small enough to mount under the seat or behind a sidecover. Electrical Connec­tion also makes a master ground block so you can route all your ground wires to a single location anywhere on the bike.

A voltmeter is the best way to make sure you don’t ask too much of your bike’s electrical system.

As long as you’re wiring things to your motorcycle, now’s a good time to think about adding a voltmeter to monitor your bike’s electrical system’s health, and let you know right away if you’re asking for more power than it can safely give you. Between ap­plications for motorcycles and cars, you’re bound to find one that fits somewhere on your bike. Aerostich (www.aero ­stich.com) sells several voltmeters, all small enough to mount on the dash or instrument panel of most motorcycles. Most auto-parts stores carry gauges from VDO (www2.vdo.com/vdo) and Stewart Warner (www.stewartwarner.com), both of which make voltmeters that can be mounted flush in a panel, or externally on a bracket.

Stretching a bike’s electrical output to the limit. Where’s the toaster oven?

By choosing the right electrical accessories to add to your motorcycle, you can enjoy the comfort of a heated vest, the sound of an MP3 player, and the safety of driving lights. By connecting them all to a single power distribution box, and using a voltmeter to monitor their power draw, you can avoid turning your bike’s wiring harness into a rat’s nest of wires and fuses. Repairs will be easier, too, as well as adding additional accessories. Just make sure you don’t add too many, though, or else you might discover one more thing cars are good for—bringing you a fresh battery from home.

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